As someone who uses and cites a lot of visual sources – maps, aerial photographs, artworks – I would find it incredibly useful to be able to open image files within Zotero tabs. Having these sources as PDFs doesn't add any value to them because they don't have text to OCR, or I am transcribing the spatial data using specialised software. I simply need to be able to flick between different sheets quickly to compare different images, and I would love it if I could do that within a program that also maintains all the citation information for when I need to footnote each item in an article.

Tropy is ok, but it doesn't allow you to open multiple images simultaneously, so you can't compare two maps or paintings of the same site, plus it doesn't do citation so you end up duplicating metadata and work. Opening them all in the default image viewer is fine, except then you end up with ten different windows with very similar file names and it becomes difficult to keep track of which image had the tiny deviation on it.

Also, coming back to the original query, photographing sources in the archives then turning them into PDFs is one thing, but using OCR on early modern English handwriting (for example) is not a simple task. Those of us who are using such sources are always doing a time-cost-benefit analysis on different ways of managing these sources, and sometimes it is easier to just keep the file in its original format.